JP3570322B2 - Method for producing chlorine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing chlorine. More specifically, the present invention relates to a method for producing chlorine in which hydrogen chloride in a gas containing hydrogen chloride is oxidized by a fixed bed reaction method having a reaction zone composed of a catalyst packed bed using a gas containing oxygen. By suppressing excessive hot spots in the catalyst packed bed and effectively utilizing the catalyst packed bed, stable activity of the catalyst is maintained, and chlorine can be obtained in a stable and high yield. The present invention relates to a chlorine production method which is extremely advantageous from the viewpoints of cost, equipment cost, operation cost, operation stability and ease.
[0002]
[Prior art]
Chlorine is useful as a raw material for vinyl chloride, phosgene and the like, and is also well known to be obtained by oxidation of hydrogen chloride. For example, as a method for producing chlorine by catalytically oxidizing hydrogen chloride with molecular oxygen using a catalyst, a copper-based catalyst called a Deacon catalyst has conventionally been considered to have excellent activity, and copper chloride and potassium chloride have been conventionally used. Many catalysts in which various compounds are added as a third component have been proposed. In addition to the Deacon catalyst, a method using chromium oxide or this compound as a catalyst and a method using ruthenium oxide or this compound as a catalyst have been proposed.
[0003]
However, the oxidation reaction of hydrogen chloride is an exothermic reaction of 59 kJ / mol-chlorine, and suppressing excessive hot spots in the catalyst packed bed reduces thermal deterioration of the catalyst and reduces the stability and ease of operation. It is important from the viewpoint of securing. Excessive hot spots can also cause runaway reactions in the worst case, and cause high temperature gas corrosion of equipment materials due to hydrogen chloride and / or chlorine.
[0004]
According to the magazine “Catalyst” (Vol. 33 No. 1 (1991)), in a reaction between pure hydrogen chloride and pure oxygen using chromium oxide as a catalyst, it is difficult to remove hot spots in a fixed-bed reaction system. Describes that it is necessary to employ a fluidized bed reactor.
[0005]
[Problems to be solved by the invention]
In such a situation, the problem to be solved by the present invention is to oxidize hydrogen chloride in a gas containing hydrogen chloride in a fixed bed reaction system having a reaction zone consisting of a catalyst packed bed using a gas containing oxygen. The method for producing a catalyst of the present invention, by suppressing excessive hot spots in the catalyst packed bed and effectively utilizing the catalyst packed bed, the stable activity of the catalyst is maintained, and chlorine is obtained in a stable and high yield. Accordingly, it is an object of the present invention to provide a method for producing chlorine which is extremely advantageous from the viewpoint of catalyst cost, equipment cost, operation cost, operation stability and ease.
[0006]
[Means for Solving the Problems]
That is, the present invention relates to a method for oxidizing hydrogen chloride in a gas containing hydrogen chloride using a gas containing oxygen by a fixed bed reaction method having a reaction zone composed of a catalyst packed bed. The present invention relates to a method for producing chlorine at a speed of 0.70 to 10 m / s.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the gas containing hydrogen chloride used in the present invention include a pyrolysis reaction and a combustion reaction of a chlorine compound, a phosgenation reaction of an organic compound, a dehydrochlorination reaction or a chlorination reaction, and hydrogen chloride generated in combustion of an incinerator. Anything can be used, including: As the gas containing hydrogen chloride, a gas having a concentration of hydrogen chloride in the gas of usually 10% by volume or more, preferably 50% by volume or more, more preferably 80% by volume or more is used. If the concentration is lower than 10% by volume, the recycling may be complicated when separating generated chlorine and / or recycling unreacted oxygen. Components other than hydrogen chloride in the gas containing hydrogen chloride include chlorinated aromatic hydrocarbons such as orthodichlorobenzene and monochlorobenzene, and aromatic hydrocarbons such as toluene and benzene, and vinyl chloride and 1,2-dichloroethane. Chlorinated aliphatic hydrocarbons such as methyl chloride, ethyl chloride, propyl chloride, allyl chloride, and aliphatic hydrocarbons such as methane, acetylene, ethylene, and propylene; and nitrogen, argon, carbon dioxide, carbon monoxide, phosgene, Inorganic gases such as hydrogen, carbonyl sulfide, and hydrogen sulfide are exemplified. In the reaction between hydrogen chloride and oxygen, chlorinated aromatic hydrocarbons and chlorinated aliphatic hydrocarbons are oxidized to carbon dioxide, water and chlorine, and aromatic hydrocarbons and aliphatic hydrocarbons are converted to carbon dioxide and water. Oxidized, carbon monoxide is oxidized to carbon dioxide, and phosgene is oxidized to carbon dioxide and chlorine.
[0008]
Oxygen or air is used as the gas containing oxygen. Oxygen can be obtained by ordinary industrial methods such as air pressure swinging and cryogenic separation.
[0009]
The theoretical molar amount of oxygen to 1 mol of hydrogen chloride is 0.25 mol, but it is preferable to supply more than the theoretical amount, more preferably 0.25 to 2 mol of oxygen to 1 mol of hydrogen chloride. If the amount of oxygen is too small, the conversion of hydrogen chloride may decrease, while if the amount of oxygen is excessive, it may be difficult to separate generated chlorine from unreacted oxygen.
[0010]
In the present invention, it is preferable that the catalyst packed bed is divided into at least two reaction zones, and the gas containing oxygen is divided into at least two and introduced. As a method of dividing and introducing the gas containing oxygen, the entire amount of the gas containing hydrogen chloride and a part of the gas containing oxygen are introduced into the first reaction zone, and the reactant and the remaining gas containing oxygen are introduced into the first reaction zone. There is a method of introducing into the reaction zone after the second reaction zone. Here, the first reaction zone means the most upstream reaction zone for the flow of the raw material gas, and the second reaction zone means the downstream reaction zone of the first reaction zone. The division amount of the gas containing oxygen introduced into the first reaction zone is 5 to 90%, preferably 10 to 80%, and more preferably 30 to 60% of the total amount. If the amount of division is too small, it may be difficult to control the temperature of the reaction zone after the second reaction zone.
[0011]
As the catalyst for the oxidation reaction of the present invention, a known catalyst known as a catalyst for oxidizing hydrogen chloride to produce chlorine can be used. Examples of the catalyst include a catalyst obtained by adding various compounds as a third component to copper chloride and potassium chloride, a catalyst containing chromium oxide as a main component, and a catalyst containing ruthenium oxide. Among them, a catalyst containing ruthenium oxide is preferable, and a catalyst containing ruthenium oxide and titanium oxide is more preferable. Catalysts containing ruthenium oxide are described, for example, in JP-A-10-182104 and EP-A-936184. Catalysts containing ruthenium oxide and titanium oxide are described, for example, in JP-A-10-194705 and JP-A-10-338502. The content of ruthenium oxide in the catalyst is preferably from 0.1 to 20% by weight. If the amount of ruthenium oxide is too small, the activity of the catalyst may be low and the conversion of hydrogen chloride may be low. On the other hand, if the amount of ruthenium oxide is too large, the price of the catalyst may be high.
[0012]
The catalyst may be used in the form of a spherical particle, a columnar pellet, an extruded shape, a ring shape, a honeycomb shape, or an appropriately sized granule which is pulverized and classified after molding. At this time, the diameter of the catalyst is preferably 10 mm or less. If the catalyst diameter exceeds 10 mm, the activity may decrease. The lower limit of the catalyst diameter is not particularly limited, but if it is excessively small, the pressure loss in the catalyst packed bed increases, so that a catalyst having a diameter of 0.1 mm or more is usually used. The term “catalyst diameter” as used herein refers to the diameter of a sphere in the case of spherical particles, the diameter of a cross section in the case of a cylindrical pellet, and the maximum diameter of the cross section in other shapes.
[0013]
The amount (volume) of the catalyst used is usually from 10 to 20,000 h ⁻¹ , expressed as a ratio (GHSV) to the supply rate of hydrogen chloride in a standard state (0 ° C., 0.1 MPa). The direction in which the raw material flows into the reaction zone may be upward or downward. The reaction pressure is usually from 0.1 to 5 MPa. The reaction temperature is preferably from 200 to 500C, more preferably from 200 to 380C. If the reaction temperature is too low, the conversion of hydrogen chloride may decrease, while if the reaction temperature is too high, the catalyst components may volatilize.
[0014]
The reaction zone consisting of the catalyst packed bed of the present invention means the whole of the packed catalyst and the packing formed only with the inert substance and / or the carrier that dilutes the catalyst. The upper and / or lower part of the reaction zone comprising the catalyst packed layer may be filled with an inert substance. However, a packed bed composed only of an inert substance is not considered as a catalyst packed bed.
[0015]
In the present invention, the gas linear velocity based on a superficial tower needs to be 0.70 to 10 m / s, preferably 0.70 to 6 m / s, and more preferably 0.70 to 3 m / s. . Thus, by suppressing excessive hot spots in the catalyst packed bed and effectively utilizing the catalyst packed bed, stable activity of the catalyst is maintained, and chlorine can be stably obtained at a high yield. Therefore, catalyst cost, equipment cost, operation cost, operation stability and ease can be ensured. In addition, the gas linear velocity based on an empty tower according to the present invention is a ratio of the total amount of supply rates of all gases supplied to the catalyst packed bed in a standard state (0 ° C., 0.1 MPa) to the cross-sectional area of the reaction tube. Means
[0016]
In the present invention, the fixed-bed reaction method having a reaction zone including at least two catalyst-packed layers in a reaction tube is performed, and chlorine is stably obtained at a high yield by effectively utilizing the catalyst-packed layers. It is preferred because it can be. As a method of forming at least two catalyst-packed layers, a method of dividing the catalyst-packed layer in the reaction tube into at least two reaction zones in the tube axis direction and filling catalysts having different activities, compositions, and / or particle sizes, Or a method in which the catalyst is filled with a filler molded only with an inert substance and / or a carrier at a different dilution ratio, or a catalyst and a catalyst diluted with a filler molded only with an inert substance and / or a carrier are filled There are ways to do that. Usually, successive reaction zones are in direct contact with each other, but an inert substance may be filled between the reaction zones. However, a packed bed composed only of an inert substance is not considered as a catalyst packed bed. The larger the number of divisions of the catalyst-packed layer, the more effectively the catalyst-packed layer can be utilized. However, industrially, it is usually 2 to 20 reaction zones, preferably 2 to 8 reaction zones, and more preferably 2 to 4 reaction zones. Performed in the reaction zone. If the number of divisions is too large, the number of types of the catalyst to be charged may increase, which may be economically disadvantageous.
[0017]
In the present invention, the catalyst packed bed is divided into at least two reaction zones in the tube axis direction, and the ratio of the first reaction zone is preferably 70% by volume or less, more preferably 30% by volume or less. In addition, the ratio of the first reaction zone is set to 70% by volume or less, preferably 30% by volume or less, and the temperature of the second reaction zone is usually 5 ° C. or higher, preferably 10 ° C. or higher than the first reaction zone. And / or molding only with a catalyst or a catalyst and an inert substance and / or a carrier such that the activity of the second reaction zone is usually 1.1 times or more, preferably 1.5 times or more higher than that of the first reaction zone. More preferably, the filled filler is filled. Here, the activity of the reaction zone (mol-HCl / ml-reaction zone-min) means the hydrogen chloride reaction activity (mol-HCl / g-catalyst-min) per unit catalyst weight and time, and the catalyst loading amount (g). ) Means the calculated value divided by the volume (ml) of the reaction zone. The hydrogen chloride reaction activity per unit weight of the catalyst and the hydrogen chloride reaction activity per hour are as follows: the ratio of the volume of the catalyst to the supply rate of hydrogen chloride in a standard state (0 ° C., 0.1 MPa) is 4400 to 4800 h ⁻¹ , This is a value calculated from the amount of chlorine generated at this time by reacting at a reaction pressure of 0.1 MPa and a reaction temperature of 280 ° C. by supplying 0.5 mol of oxygen. In the first reaction zone, the reaction rate is high because the concentrations of the reactants hydrogen chloride and oxygen are high. Therefore, for example, in a fixed bed reaction of a heat exchange system having a jacket portion, a hot spot is generated on the inlet side of the first reaction zone. On the other hand, the outlet side of the first reaction zone has a temperature close to the temperature of the heat medium in the jacket. If the ratio of the first reaction zone is larger than 70% by volume, the temperature of the reaction zone in the jacket is close to the temperature of the heat medium in the jacket, and the catalyst cannot be used effectively.
[0018]
In the present invention, the catalyst packed bed is divided into at least two reaction zones in the axial direction of the tube, and only the catalyst or the catalyst and the inert substance and / or the carrier are so selected that the thermal conductivity of the first reaction zone is the highest. It is preferable to fill the filler molded in the step (a), and it is more preferable to fill the reaction zone so that the thermal conductivity of the reaction zone gradually decreases in the gas flow direction from the first reaction zone toward the final reaction zone. Here, the final reaction zone means the most downstream reaction zone for the gas flow. The thermal conductivity of the reaction zone means the thermal conductivity of the packing filled in the reaction zone. In the reaction zone on the raw material inlet side, the reaction rate is high due to the high concentration of the reactants hydrogen chloride and oxygen, and the heat generated by the oxidation reaction is large. Therefore, by filling the reaction zone on the inlet side with a catalyst having a relatively high thermal conductivity of the catalyst, an excessive hot spot can be suppressed.
[0019]
In the present invention, the catalyst packed bed is divided into at least two reaction zones in the tube axis direction, and the activity of the reaction zone is gradually increased in the gas flow direction from the first reaction zone toward the final reaction zone. By filling the catalyst or the filler molded only with the catalyst and the inert substance and / or the carrier, the temperature difference in the continuous reaction zone can be reduced, and therefore, the operation can be performed stably and easily. Preferred because it can.
[0020]
In the present invention, the catalyst packed bed is divided into at least two reaction zones in the tube axis direction, and the activity of the final reaction zone is higher than the activity of the immediately preceding reaction zone, so that the catalyst or the catalyst is inactive. A method is preferred in which a filling molded only with the substance and / or the carrier is filled and the hot spot in the final reaction zone is lower than the hot spot in the immediately preceding reaction zone. If the activity of the final reaction zone is lower than that of the previous reaction zone and the hot spot of the final reaction zone is higher than the hot spot of the immediately preceding reaction zone, hydrogen chloride is oxidized with oxygen and converted to chlorine and water. Since the reaction is an equilibrium reaction, the conversion rate of hydrogen chloride may be low due to the chemical equilibrium composition.
[0021]
In the present invention, a method in which the catalyst packed bed is divided into at least two reaction zones in the tube axis direction, and the gas temperature at the outlet of the final reaction zone is preferably 200 to 350 ° C, more preferably 200 to 320 ° C. More preferred. When the gas temperature at the outlet of the final reaction zone is higher than 350 ° C., the reaction of oxidizing hydrogen chloride with oxygen and converting it to chlorine and water is an equilibrium reaction, so that the conversion of hydrogen chloride becomes a chemical equilibrium composition. May be dominated and lower.
[0022]
In the present invention, a method in which the temperature of the reaction zone composed of the catalyst packed bed is controlled by a heat exchange method is preferable since the reaction heat is removed well and the stability and operability of the operation are secured. The heat exchange method of the present invention means a method in which a jacket is provided outside a reaction tube filled with a catalyst, and reaction heat generated by the reaction is removed by a heat medium in the jacket. In the heat exchange method, the temperature of a reaction zone including a catalyst packed bed in a reaction tube is controlled by a heat medium in a jacket. Industrially, a fixed-tube multitubular reactor of a multitubular heat exchanger type having a reaction zone having a reaction zone composed of a catalyst packed bed arranged in series and having a jacket portion on the outside is used. You can also. As a method other than the heat exchange method, there is an electric furnace method, but there is a problem that it is difficult to control the temperature of the reaction zone.
[0023]
Examples of the heat medium include a molten salt, steam, an organic compound and a molten metal, but a molten salt or steam is preferred from the viewpoint of thermal stability and ease of handling, and from the viewpoint of better thermal stability. Molten salts are more preferred. Molten metal has problems such as high cost and difficulty in handling. Examples of the composition of the molten salt include a mixture of 50% by weight of potassium nitrate and 50% by weight of sodium nitrite, and a mixture of 53% by weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by weight of sodium nitrate. Examples of the organic compound include Dowsome A (a mixture of diphenyl oxide and diphenyl).
[0024]
In the present invention, the temperature of the reaction zone composed of the catalyst-packed bed is controlled by at least two independent temperature controls. Is preferred because As this method, a method in which the catalyst packed bed in the reaction tube is divided into at least two reaction regions in the tube axis direction and the temperature of the reaction region is controlled by a combination of a heat exchange method and a method other than the heat exchange method, at least A method in which an independent jacket portion is formed in the reaction region divided into two, and a heating medium is independently circulated to control the temperature of the reaction region, and / or the jacket portion is divided into at least two parts by a partition plate, and partitioned. A method of controlling the temperature of the reaction zone by circulating a heat medium independently in the portion where the heat medium is circulated. Although the partition plate may be directly fixed to the reaction tube by welding or the like, in order to prevent thermal distortion from occurring in the partition plate and the reaction tube, the partition plate can be substantially independently circulated within a range where the heat medium can be circulated. An appropriate distance can be provided between the partition plate and the reaction tube. It is preferable that the flow of the heat medium in the jacket flows upward from below. The more the number of reaction zones by independent temperature control, the more effectively the reaction zone can be utilized. However, industrially, usually 2 to 20 reaction zones, preferably 2 to 8 reaction zones, and more preferably 2 to 8 reaction zones. ４4 reaction zones. If the number of reaction zones to be controlled is too large, the equipment for temperature control may increase, which may be economically disadvantageous.
[0025]
In the present invention, a method in which the catalyst packed bed is divided into at least two reaction zones in the tube axis direction and the temperature of the entire reaction zone is controlled by a heat exchange method is such that the reaction heat is satisfactorily removed and the operation stability is improved. This is preferable because the simplicity is ensured.
[0026]
The inner diameter of the reaction tube is usually 10 to 50 mm, preferably 10 to 40 mm, and more preferably 10 to 30 mm. If the inside diameter of the reaction tube is too small, it may be disadvantageous because an excessive number of reaction tubes is required in order to obtain a satisfactory throughput of hydrogen chloride in an industrial reactor. If the inner diameter is too large, an excessive hot spot may be generated in the catalyst packed bed.
[0027]
The ratio (D / d) of the inner diameter (D) of the reaction tube to the catalyst diameter (d) is usually 5/1 to 100/1, preferably 5/1 to 50/1, and more preferably 5/1 to 20 /. It is one. If the ratio is too small, excessive hot spots are generated in the catalyst packed bed, or an excessive number of reaction tubes are required to obtain a satisfactory throughput of hydrogen chloride in an industrial reactor. If it is disadvantageous and the ratio is too large, excessive hot spots may be generated in the catalyst packed bed, or pressure loss of the catalyst packed bed may be large.
[0028]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Example 1
The reactor was equipped with a jacket made of a molten medium (potassium nitrate / sodium nitrite = 1/1 weight ratio) with a heating medium of 18 mm in inner diameter and 1 m in length made of a Ni reaction tube (sheath tube of 5 mm in outer diameter for temperature measurement). ) Was used. The reaction tube was filled with 99.4 g (100 ml) of a 6.6 wt% ruthenium oxide spherical granular catalyst supporting anatase crystalline TiO ₂ having a diameter of 1 to 2 mm to form a catalyst packed layer. The upper and lower portions of the catalyst packed layer were filled with 238 g and 164 g of α-Al ₂ O ₃ spheres having a diameter of 2 mm (manufactured by Nikkat Co., Ltd., SSA995), respectively. Incidentally, anatase crystalline form TiO ₂ carrying 6.6 wt% ruthenium oxide spherical particulate catalyst having a diameter of 1~2mm is prepared according to the method described in JP-A-10-338502, those used 890h again used.
Ni of 30 mm in inner diameter heated to 380 ° C. in an electric furnace with 9.4 l / min of hydrogen chloride (standard condition, hydrogen chloride: 99 vol% or more) and 4.7 l / min of oxygen (standard condition, oxygen: 99 vol% or more). It is supplied to a preheating tube (outer diameter 6 mm sheath for temperature measurement) and heated, and water is supplied to a stainless steel preheating tube having an inner diameter of 2 mm heated to 380 ° C. by an electric furnace at a temperature of 380 ° C. to vaporize water vapor. I let it. Subsequently, the preheated mixed gas of hydrogen chloride and oxygen was mixed with steam, and then flowed from the upper part to the lower part of the reaction tube in a down flow. The molar ratio of hydrogen chloride / oxygen / water is calculated to be 10/5/1, the GHSV is calculated to be 5639 h ⁻¹ , and the gas linear velocity based on an empty tower is calculated to be 1.1 m / s.
The temperature of the molten salt in the jacket was 336 ° C, and the reaction temperature of the catalyst layer was 337 ° C at the inlet, 356 ° C at the outlet, and 368 ° C for the hot spot. At this time, the pressure at the inlet of the reaction tube was 0.12 MPa-G. The outlet gas is sampled in an aqueous potassium iodide solution to absorb generated chlorine, unreacted hydrogen chloride and generated water, and the amount of chlorine produced and the amount of unreacted hydrogen chloride are determined by iodometric titration and neutralization titration, respectively. Was measured. The conversion of hydrogen chloride to chlorine was 21.5%.
[0029]
Comparative Example 1
The procedure was performed in the same manner as in Example 1 except that the catalyst amount was 48.1 g (49 ml), hydrogen chloride was 4.7 l / min, oxygen was 2.4 l / min, and water was 0.378 g / min. The molar ratio of hydrogen chloride / oxygen / water is calculated to be 10/5/1, the GHSV is calculated to be 5761 h ⁻¹ , and the gas linear velocity based on an empty tower is calculated to be 0.54 m / s.
The temperature of the molten salt in the jacket was 336 ° C., and the hot spot of the catalyst layer exceeded 380 ° C. due to the heat of reaction and became uncontrollable.
[0030]
Comparative Example 2
Example 1 was repeated except that the amount of the catalyst was 18.8 g (20 ml), hydrogen chloride was 1.9 l / min, oxygen was 0.96 l / min, and water was 0.151 g / min. The molar ratio of hydrogen chloride / oxygen / water is calculated to be 10/5/1, the GHSV is calculated to be 5724 h ⁻¹ , and the gas linear velocity based on an empty tower is calculated to be 0.22 m / s.
The temperature of the molten salt in the jacket was 336 ° C., and the hot spot of the catalyst layer exceeded 380 ° C. due to the heat of reaction and became uncontrollable.
[0031]
【The invention's effect】
As described above, according to the present invention, a method for producing chlorine, in which hydrogen chloride in a gas containing hydrogen chloride is oxidized using a gas containing oxygen, which suppresses excessive hot spots in the catalyst packed bed, By effectively utilizing the packed bed, stable activity of the catalyst can be maintained and chlorine can be obtained in a stable and high yield, so that catalyst cost, equipment cost, operation cost, operation stability and easy operation It was possible to provide an extremely advantageous method for producing chlorine from the viewpoint of properties.

Claims (3)

In a method of oxidizing hydrogen chloride in a gas containing hydrogen chloride using a gas containing oxygen by a fixed bed reaction method having a reaction zone composed of a catalyst packed bed, a gas linear velocity based on an empty tower is set to 0.70 to 0.70. A method for producing chlorine at 10 m / s. The method for producing chlorine according to claim 1, wherein the oxidation is carried out by a fixed bed reaction method having a reaction zone comprising at least two catalyst packed beds. 2. The method for producing chlorine according to claim 1, wherein the temperature of the reaction zone comprising the catalyst packed bed is controlled by at least two independent temperature controls.